Step 5 · Install New Supply Line
First, thread the larger coupling nut onto the plastic threads of the toilet's fill valve. Tighten it by hand until it is snug. Be careful not to cross-thread it. Next, thread the smaller coupling nut onto the shut-off valve. Hand-tighten this nut as well. Once both are hand-tight, use your adjustable wrench to give each nut an additional quarter-turn to a half-turn. Do not overtighten, especially the plastic connection on the fill valve.